(1) Field of the Invention
The invention relates to processes used in semiconductor manufacturing technology and more particularly to processes related to development of photoresist masks.
(2) Background of the Invention and Description of Previous Art
Integrated circuits (ICs) are manufactured by first forming discrete semiconductor devices within the surface of silicon wafers. A multi-level metallurgical interconnection network is then formed over the devices contacting their active elements and wiring them together to create the desired circuits. Patterning of the devices elements within the semiconductor surface as well as those lying above the surface such as polysilicon gates and the wiring levels and their via/contact interconnections are typically accomplished by photolithography. Indeed, the photolithography sector is perhaps the most abundant, crucial, and most sensitive in the entire chip manufacturing process. It is here where the pattern definition limits of the state of the art are defined. Photolithographic masks are formed by depositing a layer of photosensitive material, referred to as photoresist, and forming an image in the layer by selectively exposing to radiation, either by scanning, or by means of an optical mask. The image in the exposed photoresist layer is then chemically developed, to form a physical pattern.
There are three widely recognized methods of photoresist development--spin development, spray development, and puddle development. In spin development the wafer is rotated on a pedestal as the developer is dispensed onto it through a nozzle or multiple nozzles. This method is similar to the method by which the photoresist is applied. Following development, the wafers are rinsed with DI (de-ionized water), and dried while the wafer is spinning. Spray development applies a fine mist, usually from multiple nozzles, onto a single stationary wafer or onto a plurality of wafers residing in a cassette.
More recently, static "puddle" development has become widely used. In this new technique, the developer is slowly dispensed onto the surface of a wafer. The wafer may be rotated at slow speed as the developer is dispensed. Once the developer has been delivered, the wafer remains stationary for the duration of the development cycle, typically for about 60 seconds. After development the wafer is rinsed and spun dry. The newest resist formulations are optimized for puddle processing, resulting in improved control of uniformity and minimal consumption of chemicals (See El-Kareh, B., "Fundamentals of Semiconductor Processing Technologies", Kluwer, Boston, (1995), p210-211).
Matsuoka, U.S. Pat. No. 5,194,350 shows an apparatus for developing an exposed photo emulsion on a chromium layer on a glass substrate. The developer solution is dispensed into a developing vessel immersing the substrate which rests, within the vessel, upon a rotatable table. The substrate is not rotated or spun during development but is subsequently spun in a rinse and dry step.
Kishimura, U.S. Pat. No. 5,591,654 deposit thick (3-6 micron) photoresist layers which are patterned to serve as high energy ion implantation masks. After exposure, the thick photoresist layers are baked and developed by a puddle development process for 100 seconds using an NMD developer. Fukuda, U.S. Pat. No. 4,564,280 shows an apparatus which includes a rotatable table and developer dispensing arm which is used for static puddle development. In use developer is dispensed from nozzles while the wafer rotates at a relatively high speed. At the end of the dispensing, the wafer is rotated one more turn at reduced speed and then stopped. The wafer remains stopped for the remainder of the development cycle. Usujima, U.S. Pat. No. 5,789,141 cites a method of photoresist development wherein the developer is placed upon a wafer and retained by surface tension. However, there is no suggestion that the developer, so placed, undergoes any manner of agitation.
Okazaki, et. al., U.S. Pat. No. 5,773,200 cites a positive resist composition developed by development in an aqueous solution of TMAH (tetramethyl ammonium hydroxide).
Thompson, U.S. Pat. No. 5,292,605 cites multiple spray/puddle steps for developing a photoresist image. An optical endpoint controller is used to control the development time. Developer is sprayed onto the wafer and allowed to puddle. After a time interval more developer is sprayed onto the wafer, forming a new puddle. This method, although providing intermittent replenishment on the wafer surface during the development cycle, nevertheless wastes expensive developer.
The effectiveness of any development recipe can be ascertained by the measurements of the dimensions and integrity of the resultant photoresist images, measurements of defects introduced by the process, and the time efficiency and the process complexity and cost. Once a procedure has been established, optimization procedures are generally employed to tweak process times, temperatures, rotational speeds and the like to give the best quality images with minimal cycle time and cost. An example of a photoresist development process which uses the puddle method is illustrated in Table I. The process utilizes two static puddle development periods with a developer spin off step between. Prior to each development period, the developer is dispensed onto the rotating wafer to form a puddle. The wafer is then stopped and is allowed to remain motionless for the duration of the development period. After the development period is over, the wafer is rotated and the developer puddle is spun off the wafer. A two step rinse and spin dry process then follows to complete the process. The total cycle time for the process as shown is approximately 3 minutes.
TABLE I ______________________________________ Reference Process Step Time.sup.1 Rotation.sup.2 Accel..sup.3 Operation ______________________________________ 1 3.5 1,500 10,000 Rotate Wafer 2 3 1,500 10,000 Dispense DI Water 3 3 1,500 10,000 Spin Dry 4 3 0 1,000 Idle 5 0.1 10 1,000 Dispense Developer 6 1.5 60 1,000 Dispense Developer 7 25 0 1,000 First Develop (system exhaust off) 8 2 1,000 1,000 Spin Dry (system exhaust back on) 9 5 0 1,000 Air Vent (Prime developer nozzle) 10 2 60 1,000 Dispense Developer 11 3 0 1,000 Auto Damper (system exhaust off) 12 35 0 1,000 Second Develop 13 5 0 1,000 Idle 14 10 2,000 10,000 DI Water Rinse (system exhaust back on) 15 15 1,200 10,000 DI Water Rinse 16 6 600 10,000 DI Water Rinse 17 3 5,000 10,000 Spin Dry 18 3 3,500 10,000 Spin Dry 19 1 1,000 10,000 Spin Dry 20 5 0 10,000 Idle Wash 21 10 2,000 10,000 DI Water Rinse 22 15 1,200 10,000 DI Water Rinse 23 6 600 10,000 DI Water Rinse 24 3 5,oo0 10,000 Spin Dry 25 6 4,000 10,000 Spin Dry 26 4 3,000 10,000 Spin Dry 27 2 2,000 10,000 Spin Dry 28 2 1,000 10,000 Spin Dry 29 2.5 0 10,000 Stop Total 184.6 ______________________________________ .sup.1 In seconds .sup.2 In rpm (revolutions per minute) .sup.3 In rpm/sec.
Although the development process shown in Table I, is workable, It would be desirable to reduce the turn around time and therefore speed production. In addition, it would also be desirable to improve the dimensional uniformity of pattern features across a wafer and from wafer to wafer as well to reduce process related defect degradation.